1. Technical Field
The present disclosure relates to an information recording and reproducing apparatus and an information recording and reproducing method, both capable of performing recording compensation more accurately to an information recording medium having an information recording surface to which information is optically recordable, the recording compensation being performed for realizing high density recording more stably.
2. Description of Related Art
Conventionally, information recording media such as DVDs (Digital Versatile Discs) and BDs (Blu-ray (registered trademark) Discs) are used as recording media aimed at general users for storing video or data. In recent years, BDs have come to be used in data archivers for storing important data for an extended period of time with a highly reliable system. Data archivers are a product that is mainly available for business use, and are required to have higher density in order to allow more data to be stored.
In such an information recording medium, information is recorded by forming a recording mark and a space over a recording layer of the information recording medium.
When the information in the information recording medium is reproduced, the recording mark and the space formed over the recording layer are irradiated with laser light of low output power, and a reproduced signal is obtained based on a difference between optical characteristics, e.g., reflectance ratios, of the recording mark and the space. By performing signal processing on the reproduced signal, the recorded information is reproduced.
When information is recorded to the information recording medium, based on information to be recorded, the recording layer is irradiated with a recording pulse obtained by intensity modulation to laser light and a recording mark is recorded.
An information recording and reproducing apparatus that performs recording and reproducing on the information recording medium performs recording compensation of adjusting a leading edge position and a trailing edge position of the recording mark such that errors in reproduced signals obtained by reproducing the recorded recording mark are reduced.
The recording compensation is particularly required in a recording density in which a length of a space between recording marks is short. In the recording density in which the length of a space between recording marks is short, heat generated when a recording mark is formed is not sufficiently reduced at a space section, and affects a temperature rise at a leading edge of a succeeding recording mark. Adversely, the heat at the leading end of the succeeding recording mark affects the cooling of the heat at a trailing edge of the preceding recording mark. Such an influence is referred to as thermal interference, which depends on a length of the space. In the recording compensation, a shape of a pulse of recording laser is finely adjusted depending on the length of the space in order to compensate positions of the edges of the recording marks that change depending on the thermal interference.
Further, as lengths of the recording mark and the space are reduced, amplitude of a reproduced signal is also reduced, and a difference is produced between reproduced signals according to a combination of the recording mark and the space due to an influence of symbol interference. For example, even if the length of the recording marks is the same, depending on a difference between lengths of spaces before and after the recording marks, reproduced signals in particular at the edge portions of the recording marks are detected differently. Therefore, it is considered to be effective to employ a method such as PRML (Partial Response Maximum Likelihood) as a method of reproduced signal processing. By performing waveform equalization of the reproduced signals by the PRML method to reduce the influence of the intersymbol interference, it is possible to perform recording compensation more accurately.
Unexamined Japanese Patent Publication No. 2011-23069, for example, discloses one example of a method of detecting an edge shift which is displacement between edge positions of recording marks in order to perform waveform equalization of reproduced signals by the PRML method to perform recording compensation.
In Unexamined Japanese Patent Publication No. 2011-23069, focusing on edges of a recording mark in a maximum likelihood bit stream that is a reproduced signals decoded by the PRML method, an error bit stream is generated, which is a bit stream that is most susceptible to error in which a bit of a maximum likelihood bit stream at the edge portion or a bit of a maximum likelihood bit stream in an entire recording marks including edge portions shifts, and the edge shift is evaluated based on an Euclidean distance difference between a reproduced signal and target signals respectively corresponding to the maximum likelihood bit stream and the error bit stream.
With this, in recording compensation in recording density of about 31 GB in the case of a BD, it is possible to directly detect an edge shift of an edge portion using either of a reproduced signal at an edge portion of a recording mark as a target of recording compensation, or a reproduced signal in a range of the length of a space that is adjacent to this recording mark.